Antonio, if you don't have a nutritionist, you should get one immediately. What you're describing is horrifying and heading toward illness and death.
If you can't tolerate a lot of different foods, you can supplement with nutritional powders and liquid drinks. You absolutely need to keep your nutritional profile in the best number ranges. You can't shrink or stretch your stomach. Those are myths designed to accompany eating disorders. If you starved to death, it wouldn't be your stomach that was affected first. It would be organ failure from lack of nutrition, necessary vitamins and minerals. It has NOTHING to do with the size of your stomach, and neither does the urge to eat. You feel stuff in your stomach, but these things originate in your brain and have effects on your pineal gland and other parts of your brain.
Stop eating when you feel full. Eat slowly. Chew well. Put your utensils down between bites. These are essentials to cultivate rather than fear of stretching your stomach.